Study of the Surface Chemical Reactions of Thiophene with Ag/Titania by the Complementary Temperature-Programmed Electron Spin Resonance, Temperature-Programmed Desorption, and X-ray Photoelectron Spectroscopy: Adsorption, Desorption, and Sorbent Regeneration Mechanisms

Abstract

Reaction of thiophene with the ultradeep desulfurization sorbent Ag/titania under ambient conditions was studied by the multiple complementary temperature-programmed techniques: electron spin resonance (ESR), high-vacuum temperature-programmed desorption (HV-TPD), high-vacuum temperature-programmed reaction spectroscopy (HV-TPRS) and by X-ray photoelectron spectroscopy (XPS). Sorption of thiophene at 25−75 °C proceeds via strong molecular adsorption. Decomposition of the adsorption complex “Ag/titania + thiophene” occurs in a stage-wise fashion. At ∼75 to 175 °C, the adsorption complex decomposes without reaction with molecular oxygen. Adsorbed thiophene molecularly desorbs at ∼90 °C (desorption energy = 105 kJ/mol). At ∼75 to 175 °C, the nonoxidative pyrolysis of the adsorption complex with the C−S scission and desorption of butadiene proceeds. At ∼225 to 525 °C, molecular oxygen participates in thermal decomposition of the adsorption complex to form SO2. Under the deficiency of O2, the hydrogen-lean “coke” C x H y (x ≫ y) is formed. The combination of temperature-programmed ESR, TPD/TPRS, and XPS is well-suited to investigate the molecular-level mechanisms of adsorption, desorption, and surface chemical reactions of the sulfur-containing adsorbates.

Effects of alumina phases as nickel supports on deep reactive adsorption of (4,6-dimethyl) dibenzothiophene: Comparison between γ, δ, and θ-alumina

“…The order of adsorption strength on nickel surface is: nitrogenated hydrocabons > oxygenated hydrocabons > aromatics (including sulfur compounds) > olefins > paraffins [46]. It should be noted that saturated hydrocarbons (paraffins and cycloparaffins) do not adsorb on the nickel surface at temperatures between 366 and 533 K [47,48]. Therefore, when unsaturated hydrocarbons such as aromatic intermediates resulting from sulfur compounds or olefins formed by cracking of the solvent molecules are adsorbed on nickel surface and the surface is heated, the adsorbed molecule rather than being desorbed reversibly decomposes to evolve hydrogen.…”

Understanding the dispersion of Ag on high surface area TiO2 supports using XPS intensity ratios

“…As a result, a number of techniques have been used for characterizing this system. Transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), X-ray diffraction (XRD), and oxygen chemisorption (OC) have been previously employed in an attempt to elucidate the surface behavior of this adsorbent [1][2][3][4]. Silver atom dispersion and crystallite size are two crucial factors that influence capacity and selectivity of the adsorbent.…”

Desulfurization of JP-8 jet fuel: challenges and adsorptive materials

“…It has been used primarily loaded with silver for adsorptive desulfurization. 23,[80][81][82][83][84][85] Density functional theory has been used to better understand the interactions that organosulfur compounds have with the surface of titania. Song and coworkers studied the interaction between thiophene and the (001) surface of anatase TiO 2 (Fig.…”